Introduction. The religious factor -- The scientific factor -- Phases of presocratic philosophy -- Problems of translation -- References and abbreviations -- Early religious thought. In Olympian perspective -- Chthonic religion and mystery cults -- The reflective mood -- Xenophanes -- The scientist-philosophers of Miletus. Thales -- Anaximander -- Anaximenes -- Heraclitus. The Eleatic school. Parmenides -- Zeno -- Melissus -- Qualitative pluralism. Empedocles -- Anaxagoras -- Atomism. Leucippus -- Democritus -- Pythagoreanism. Aspects of the doctrine -- The Pythagorean symbola -- From the golden verses -- Philolaus -- The Sophists. Protagoras -- Gorgias -- Fragments from other Sophists -- Hippocratic medical philosophy. From The sacred malady -- From The nature of man -- From On ancient medicine -- Precepts and aphorisms